1. Field of the Invention
The invention relates generally to a subsea riser and more specifically to a breech lock connector between portions of the riser.
2. Background of the Invention
Subsea Riser assemblies allow operations on subsea wells and other subsea equipment from a platform at the surface. Subsea Riser assemblies typically have a plurality of tubular-shaped riser segments that are connected together to make-up the full length of the riser assembly. Operators have attempted numerous connection assemblies in order to connect the ends of the riser segments and make a complete riser assembly reaching from the platform to the subsea well. Some examples of couplings between riser segments include flanged type couplings, clamp type couplings, and dog type couplings. These types of couplings are generally large and heavy because of the loads that are transmitted through the couplings from one riser segment to another.
Another type of coupling used in the past is a threaded coupling. Threaded couplings are generally smaller than other types of couplings, which is advantageous to operators on the platform. Typical threaded couplings include an arrangement having a male pin section attached to an end of a riser segment and a female box attached to an end of another riser segment that engages the threads of the male pin. In some of these threaded couplings, the male and female ends are rigidly attached to the riser segments, which requires that one of the entire riser segments is rotated relative to the other in order for the riser segments to be connected. In other versions, the threaded female end is a separate member that fits between the pins on the two riser segments. The separate member slides over one of the pins, and the inside threading engages the external threading of the other pin. Rotating the separate member relative to the threading on the exterior of one of the pins causes the separate member to compress and engage the other pin in order to connect to the two riser segments. Another threaded coupling includes a union nut that is attached to one of the riser segments and a male pin that is attached to the other riser segment. The union nut is free-spinning relative to the first riser segment. When the union nut spins relative to the male pin, the union nut pulls the two riser segments together and thereby connects the riser segments.
While threaded connections are less bulky and smaller than other couplings, the torsional forces experienced by the riser assembly is transmitted through the threads at each connection from one riser segment to another. The transmission of torque through the threads introduces the possibility of the threads unscrewing or backing off, and thereby causing the riser segments to disengage or causing the connector assembly to lose its sealing properties between riser segments. Additionally, repeated make-up and breakout of the connection may result in damage to the threads and the seals associated with the threaded connections.